The advantages of fiber interferometer gyros over mechanical gyros and ring laser gyros have been recognized. Briefly, the mechanical gyros have shown a tendency for parts to wear and fail; they are relatively bulky and heavy; and, at times, their power consumption rates are excessive, to name a few. Some of the inherent limitations of the mechanical devices were thought to be partially remedied by the ring laser gyro. The ring laser gyro is a digital output device with no spinning mass element to rebalance. The ring laser also is capable of handling high rate inputs. It is close to being an ideal strap down sensor, easily interfaced with a digital computer and it is relatively rugged, long-lived, and reliable due to its simple optical quality construction. However, at the present state of development, ring laser gyros suffer limitations due to nonlinear "pulling" and "lock-in" at low rotation rates. In addition, the ring laser gyro production cost appears to be significantly higher than the emerging family of fiber interferometer gyros which are now in research and development.
Fiber optic gyros have been proposed by V. Vali and R. W. Shorthill as Fiber Laser Gyroscopes at the East Coast Conference of the SPIE in Reston, Virginia on Mar. 22 and 23 of 1976. In a follow-up article in the Proceedings of Conference on Fibers Integrated Optics a typical fiber ring interferometer was disclosed. It used an arrangement of conventional beamsplitters and lenses to introduce clockwise and counterclockwise pulses in a coiled optical fiber. The interference patterns were observed and rotation rates could be determined. Improvements over this typical fiber ring interferometer were disclosed in the referenced applications to provide for more responsive rotation rate indications.
The typical interferometer of Vali and Shorthill and the improvements of the applications have sensitivities which depend on the size of the area encircled by the optical fiber. Coiling the fiber around this area multiplies the sensitivity of the interferometer by the number of turns. A limitation is apparent in that the attenuation figure of the fiber limits its total length and, hence, imposes a limit on the interferometer's sensitivity. Thus, there is a continuing need in the state-of-the-art for a means to improve fiber interferometer gyro sensitivity without unduly complicating this otherwise straightforward device.